The present invention relates to the capping of printheads of inkjet cartridges used in inkjet printers, and in particular to an improved method and apparatus for capping a plurality of cartridges.
Inkjet cartridges are now well known in the art and generally comprise a body containing an ink supply and having electrically conductive interconnect pads thereon and a printhead for ejecting ink through numerous nozzles in a printhead. In thermally activated inkjet cartridges, each cartridge has heater circuits and resistors which are energised via electrical signals sent through the interconnect pads on the cartridge. Each inkjet printer can have a plurality, often four, of cartridges each one having a different colour ink supply for example black, magenta, cyan and yellow, removably mounted in a printer carriage which scans backwards and forwards across a print medium, for example paper, in successive swaths. When the printer carriage correctly positions one of the cartridges over a given location on the print medium, a jet of ink is ejected from a nozzle to provide a pixel of ink at a precisely defined location. The mosaic of pixels thus created provides a desired composite image.
Inkjet cartridges are increasingly becoming more sophisticated and complex in their construction and longer lifetimes are also required of cartridges, particularly those for use with printers having an off-carriage ink reservoir which replenishes the cartridge s ink supply. This has lead to greater sophistication in the so-called xe2x80x9cservicingxe2x80x9d of cartridges by a printer. It is normal for printers to have a service station at which various functions are performed on the cartridges while they are mounted in the printer carriage such as wiping, spitting and capping, see for example U.S. Pat. No. 5,585,826. Wiping comprises moving a wiper of a specified material across the printhead of a cartridge to remove paper dust, ink spray and the like from the nozzle plate of the printhead. Spitting, ejecting ink into a spittoon in the service station, is performed to prevent ink in nozzles which have not been fired for some time from drying and crusting.
Cartridges are capped by precisely moving the printer carriage, and often the cap too, within the service station, so that the cap mates with the printhead of the cartridge and forms a seal around the nozzle plate. Capping prevents ink on the printhead and in the nozzles from drying by providing the correct atmosphere around these components and thus reduces the risk of crusting and ink plug formation in the nozzles. Also the cartridge can often be primed while in the capped position by the application of a vacuum through the cap. It can thus be seen that an effective seal must be formed between the printhead and the cap to facilitate these functions. Caps are usually formed of a resiliently deformable material such as rubber and in use are ideally pressed against a printhead of a cartridge with a substantially constant force, the capping force, chosen so as to achieve an effective seal with the printhead. While this is relatively easily achieved for a printer carriage having a single cartridge, ensuring that all the cartridges of a printer carriage having a plurality of cartridges are effectively capped is considerably harder. A number of arrangements are known, see for example U.S. Pat. No. 5,563,638, in which a plurality of caps are mounted on a spring-loaded gimbal mechanism in an attempt to achieve a constant capping force between each of the caps and its respective printhead. However, manufacturing tolerances unavoidably cause there to be differences between each cap and cartridge pair and the remaining pairs. These differences can often result in different capping forces for each cap and cartridge pair so that some pairs receive insufficient capping force and others receive too great a capping force which may damage the printhead. In an attempt to alleviate these problems an improved cap has been designed as disclosed in the commonly assigned, issued U.S. Pat. No. 5,448,270 by Osbourne, which is incorporated herein by reference. Although the cap described in ""270 is effective in achieving a substantially constant low capping force over a greater deflection for each cap and cartridge pair than prior caps, it has been found that there is nevertheless still undesirable and unpredictable interaction between different pairs of caps and cartridges which affects their accurate mating.
There is provided apparatus for capping a plurality of printheads of inkjet cartridges held within the printer carriage of an inkjet printer, the apparatus comprising a service station carriage having a plurality of capping means, each for capping the printhead of an inkjet cartridge, a service station assembly in which the service station carriage is mounted and which is movable in a capping direction between a first position at which the cartridges are not capped and a second position at which the cartridges are capped, wherein relative movement in the capping direction between the plurality of cartridges and the plurality of capping means is arrested by the abutment of the service station carriage against the printer carriage. By controlling the distance between the service station carriage and the printer carriage the capping forces between a particular capping means and respective printhead are determined only by the tolerances related to the particular capping means and printhead pair and not by those related to other pairs of capping means and printheads mounted within the same service station and printer carriages.
Although the service station carriage may be rigidly mounted within the service station assembly, preferably the service station carriage is resiliently biased in the capping direction within the service station assembly by biasing means and the biasing means exert a force on the service station carriage which is greater than the total expected forces between the plurality of cartridges and the plurality of capping means so as to ensure abutment between the service station carriage and the printer carriage. In a preferred embodiment, the service station carriage is gimbal mounted within the service station assembly.
Advantageously, an uppermost side of the service station carriage comprises a plurality of mechanical stops for abutment with a corresponding plurality of mechanical stops located on a lowermost side of the printer carriage. These mechanical stops abut when the service station carriage and printer carriage are moved towards each other and thus act so as to arrest relative movement in the capping direction between the plurality of cartridges and the plurality of capping means.
In a specific embodiment, the service station carriage comprises at least three mechanical stops. A first male mechanical stop extending upwardly from the service station carriage in the form of a pin to interact with a first female mechanical stop on the printer carriage in the form of an inverted pyramid. The interaction of these two mechanical stops substantially inhibits relative translational movement between the service station carriage and the printer carriage within a plane perpendicular to the capping direction. A second male mechanical stop, also in the form of a pin, extending upwardly from the service station carriage interacts with a second female mechanical stop on the printer carriage so as to substantially inhibit relative rotational movement between the service station carriage and the printer carriage within a plane perpendicular to the capping direction. A third mechanical stop, or advantageously third and fourth mechanical stops interact with a third and fourth mechanical stop on the printer carriage so as to prevent relative movement between the service station carriage and the printer carriage solely in the capping direction.
Although the capping apparatus provided by the present invention may be advantageously utilised with caps which are designed to be mounted to the printer service station for the life of the printer, preferably the caps are mounted on a service module which is easily removable from the service station carriage by a user of the printer. Removable service modules allow the caps to be exchange frequently, for example every time a cartridge is replaced its associated service module may also be replaced. This ensures that the cap of the service module does not deteriorate in performance unduly.
To facilitate removable service modules, the service station carriage preferably comprises a plurality of slots each for slidably receiving a service module. Each slot of the service station may comprise means for urging the service module against a datum within the service station carriage with a force greater than the total expected forces between the plurality of cartridges and the plurality of capping means. This ensures that the service module is not dislodged from its datum position during a capping operation.
According to a further aspect of the present invention there is provided apparatus for capping a plurality of printheads of inkjet cartridges mounted within a carriage, comprising a plurality of capping means mounted on a common support member and biasing means for biasing the common support member towards the plurality of printheads. Relative movement in the capping direction between the capping means and the printheads is limited by a mechanical stop positioned so that the distance between each of the capping means and a respective printhead when the mechanical stop is encountered is such that an effective seal is formed between the capping means and the printhead and wherein the biasing force provided by the biasing means is sufficiently large to ensure that in use the mechanical stop is encountered.
According to a still further aspect of the present invention there is provided a method of capping a plurality of inkjet cartridges held within the carriage of an inkjet printer, each cartridge having a printhead for ejecting ink. The method comprising the steps of moving the printer carriage within the printer to a service area, moving a service station carriage having a plurality of capping means towards the printer carriage with a force greater than the total expected capping forces between the plurality of cartridges and the plurality of capping means until the service station carriage abuts the printer carriage.
A more complete understanding of the present invention and other objects, aspects, aims and advantages thereof will be gained from a consideration of the following description of the preferred embodiment read in conjunction with the accompanying drawings provided herein.